Polyimide films are frequently used in a variety of high temperature applications (up to 800.degree. F.). However, adhesives for use with such films at high temperatures are virtually unknown.
In a paper entitled "600.degree. F. Thermoplastic Polyimide Adhesive" presented at the 29th National SAMPE Symposium, Apr. 3-5 1984. R. T. Alvarez describes the use as adhesives for aluminum, titanium and polyimide glass composites of polyimides from a reaction between a carboxy-terminated bisimide monomer and an aromatic diamine. The polyimides, termed by the author as exchange polyimides, are synthesized by first reacting a dianhydride such as 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride (BTDA) with an oxoimine. The carboxy-terminated bisimide monomer is further reacted with aromatic diamines in a solvent and polymerized to an imide by an exchange reaction. The author's FIG. 3 describes some of the chemical reactions which occur during this exchange reaction. According to Alvarez, the exchange polyimides do not generate volatile by-products normally associated with linear aromatic condensation polyimides, and thus large void-free bond areas can be achieved using low pressure and low cure temperatures. An exchange polyimide from 2,2-bis[(4-aminophenoxy)phenyl]hexafluoropropane and BTDA was indicated to give the highest oxidation resistance at temperatures up to 700.degree. F.